Method for determining the current pre-pressure of a diaphragm pressure expansion vessel

Abstract

The invention relates to a method for determining the current actual pressure p IST a diaphragm pressure expansion vessel (1) which has an interior space with a known nominal volume V N which is separated by a membrane (2) into a gas space (3) and a liquid space (4), wherein the filling volume of the liquid space (4) is unknown, wherein the gas space (3) of the membrane pressure expansion vessel (1) is connected to a testing device (8) and the pressure in the gas space (3) is changed by means of the testing device (8). It is intended that the test device (8) first measures the current pressure p1 in the gas space (3), then the test device (8) adds a gas volume V z with a pressure p z and thereby a pressure increase in the gas space (3) to a pressure p2 is generated, whereby finally from the values ​​p1, p2, p z , V Z and V N the actual form p IST is calculated.

Description

[0001] The invention relates to a method for determining the current actual pressure p IST a diaphragm pressure expansion vessel, which has an interior space with a known nominal volume V N which is separated by a membrane into a gas and a liquid space, wherein the filling volume of the liquid space is unknown, wherein the gas space of the membrane pressure expansion vessel is connected to a testing device and the pressure in the gas space is changed by means of the testing device, as well as a testing device for carrying out this method.

[0002] Diaphragm expansion vessels are typically used in closed heating, cooling, domestic hot water, and solar systems. The volume change caused by temperature changes in the liquid heat transfer medium is absorbed or released by a diaphragm expansion vessel. For this purpose, the diaphragm expansion vessel is divided internally by an elastic diaphragm into a variable-volume gas and liquid chamber.

[0003] The pressure prevailing in the gas chamber of a diaphragm expansion vessel not filled with heat transfer fluid (e.g., at the time the vessel is installed in the system, before the liquid chamber is connected to the system's piping system) is generally referred to as the pre-pressure. This pre-pressure must be adjusted to the specific system conditions, with the static system height being relevant, for example. This pre-pressure is a key parameter for the proper functioning of a diaphragm expansion vessel.

[0004] Over the course of operation, the gas in the gas chamber, usually nitrogen, slowly diffuses through the membrane into the heat transfer medium. Thus, the pre-pressure decreases over time, and gas must be refilled during maintenance work to ensure proper functioning of the diaphragm expansion vessel.

[0005] To check and, if necessary, correct the pre-pressure of a diaphragm pressure expansion vessel, it has been necessary in practice to measure the current pre-pressure on a diaphragm pressure expansion vessel that is pressureless on the liquid side and to correct it if necessary. To do this, the diaphragm pressure expansion vessel must be separated from the system and the liquid chamber emptied, which is complex and disadvantageous. For example, if water is used as the heat transfer medium, the water drained for the pre-pressure test usually has to be drained off and replaced with fresh drinking water, which leads to an undesirable increase in resource requirements. Another disadvantage is that the system water should be replaced with fresh drinking water as little as possible to avoid oxygen ingress and scale formation in the system. Therefore, complex water treatment is required, at least for larger systems. If a water-glycol mixture is used as the heat transfer medium (e.g.In solar systems, the heat transfer fluid must be collected and then pumped back into the system, and the system vented. Using a water-glycol mixture therefore requires even more testing effort.

[0006] To avoid these disadvantages, DE 10 2016 012 700 B4 discloses a method for measuring the actual pre-pressure of a diaphragm pressure expansion vessel with an unknown liquid-side filling and with knowledge of the nominal volume of the diaphragm pressure expansion vessel. The diaphragm pressure expansion vessel is connected to two controllable valves and a pressure transducer via a connecting line. A valve is used to release a gas volume from the diaphragm pressure expansion vessel into the ambient air via a volume flow meter or a measuring nozzle until the pressure measured at the pressure transducer has decreased from the start pressure to the final pressure of the measurement. The actual pre-pressure is calculated using the measured values ​​thus determined and the known atmospheric pressure. Furthermore, this document discloses a device suitable for carrying out this method for measuring the actual pre-pressure of a diaphragm pressure expansion vessel.Since the gas extraction from the diaphragm expansion vessel inevitably reduces the pre-pressure, it is usually necessary to refill the vessel with gas after the measurement procedure has been completed. If the actual pre-pressure is very low, the measurement procedure cannot be used, as sufficient gas volume cannot be extracted.

[0007] The object of the invention is to provide an improved solution for determining the current actual pre-pressure of a diaphragm pressure expansion vessel, which is independent of the actual pressure conditions in the diaphragm pressure expansion vessel and in which the diaphragm pressure expansion vessel does not have to be separated from the associated system and emptied.

[0008] This object is achieved according to the invention in a method of the type described above in that the test device first measures the current pressure p1 in the gas space, then the test device supplies the gas space with a gas volume V z with a pressure p zand thereby a pressure increase in the gas space to a pressure p2 is generated, whereby finally from the values ​​p1, p2, p z , V z and V N the actual form p IST is calculated.

[0009] By introducing a defined volume of gas and the resulting pressure increase in the gas chamber of the diaphragm pressure expansion vessel, the current actual pre-pressure can be determined independently of the current pressure conditions in the diaphragm pressure expansion vessel. This does not require draining water from the diaphragm pressure expansion vessel. Before starting the measurement, the vessel's water connection is conveniently shut off to maintain a constant volume ratio between the gas chamber and the water chamber for the calculation and adjustment steps.

[0010] When determining the actual pre-pressure, any small temperature differences that may occur, which have little influence on the volume ratio, are neglected. However, they can generally be taken into account through more complex calculations and temperature measurements. After connecting the test device, the pressure p1 in the gas chamber of the diaphragm pressure expansion vessel is measured at the beginning of the test. In the next step, a known gas volume V is added to the gas chamber. Z with a known pressure p Z and the resulting pressure increase to a pressure p2 is measured. The supplied gas quantity V Z with the pressure p Z It is precisely defined what can be realized in different ways.

[0011] From the known pressure values ​​and volumes, the actual pre-pressure p IST as follows:

[0012] For isothermal changes of state and constant number of gas particles (gas quantity), Boyle and Mariotte’s law applies: p⋅V=constant

[0013] So: pIST⋅VN=p1⋅V1−p2⋅V2

[0014] After the measurement has started, a gas volume V Z with a pressure p Z into the gas chamber of the diaphragm pressure expansion vessel, which, however, cannot expand due to the compressibility of the water. The pressure increases and the gas volume remains constant, thus: V2=V1

[0015] The supply of gas volume V Z with a pressure p Z is taken into account in (1) as follows: pIST⋅VN=p1⋅V1+pZ⋅VZ=p2⋅V2

[0016] From (2) and (3): pZ⋅VZ=V1⋅(p2−p1) From (4):V1=V2=pZ⋅VZp2−p1

[0017] From (3) and (5): pIST⋅VN=p2⋅pZ⋅VZp2−p1

[0018] From (6): pIST=p2VN⋅pZ⋅VZp2−p1 p IST : current actual form (to be determined) V N : Nominal volume of the MAG (known) p1: Pressure in the gas chamber at the start of the measurement (measured) V1: Volume of gas space at start of measurement (unknown) p2: Pressure in the gas chamber at end of measurement (measured) V2: Volume of gas space at end of measurement (unknown) V Z : Gas volume supplied (known) p Z : Pressure of the supplied gas volume (known)

[0019] Various variants are possible for the defined supply of a gas volume.

[0020] According to a first embodiment, the pressure in the gas chamber is increased by the test device to a predetermined pressure p2 and the supplied gas volume V z measured or determined.

[0021] According to a second embodiment, it is provided that the test device supplies the gas space with a predetermined gas volume V Z and then the increased pressure p2 in the gas space is measured.

[0022] To solve the problem, a test device is also required to determine the current actual pressure p IST a diaphragm pressure expansion vessel for carrying out the above-described method with a measuring chamber having a pressure sensor, wherein the measuring chamber is connected to a connecting line for connection to the gas space of the diaphragm pressure expansion vessel and to a gas supply device, wherein an electronic measuring and evaluation unit is provided which interacts with the pressure sensor and the gas supply device and is designed to carry out the above-described method.

[0023] It is advantageous for the gas supply device to be a compressor or a piston pump. When using a compressor, the supplied gas volume is preferably determined via the compressor characteristic curve and the backpressure in the gas chamber. If the gas volume is supplied via a piston pump, the piston chamber is subjected to either ambient pressure or a defined pressure. The supplied gas volume is determined via the number of piston strokes or the piston stroke position and the backpressure of the gas chamber.

[0024] Alternatively, the gas supply device is provided as a gas cartridge connected to a solenoid valve. The supplied gas volume is determined by the switching times of the solenoid valve to the gas cartridge and by the pressure in the gas cartridge and the counterpressure in the gas chamber.

[0025] All of the aforementioned embodiments of the gas supply device can optionally be provided with a volume flow measuring unit and / or a nozzle, which increases the accuracy of the introduced gas quantity measurement.

[0026] The invention is explained in more detail below with reference to the drawings, which show a simplified schematic diagram in Fig. 1 a diaphragm pressure expansion vessel with a first test device, Fig. 2 a diaphragm pressure expansion vessel with a second test device, Fig. 3 a diaphragm pressure expansion vessel with a third test device and Fig. 4 a diaphragm pressure expansion vessel with a fourth test device.

[0027] A diaphragm pressure expansion vessel is generally designated 1 in the drawings. It has an interior with a known nominal volume V Nwhich is separated by a membrane 2 into a gas chamber 3 and a liquid chamber 4. The liquid chamber 4 is connected via a lockable connection piece 5 (e.g., with a cap valve not shown) to a closed pipe network of a heating, cooling, domestic water, and solar system (also not shown). The current filling volume of the liquid chamber 4 is unknown.

[0028] The diaphragm pressure expansion vessel 1 has a gas filling valve 6 connected to the gas chamber 3, to which a connecting line 7 of a test device, generally designated 8, is connected. The test device 8 has a measuring chamber 9 with a pressure sensor 10 and, if appropriate, a temperature sensor 11, wherein the measuring chamber 8 is connected to the connecting line 7 for connection to the gas chamber 3 of the diaphragm pressure expansion vessel 1 and to a gas supply device. The gas supply device is in the embodiment according to Fig. 1 is designed as a gas cartridge 13 connected to a solenoid valve 12. A pressure regulator 14 is arranged between the gas cartridge 13 and the solenoid valve 12. The solenoid valve 12 is connected to a further pressure sensor 15 and establishes the connection from the gas cartridge 13 to the measuring chamber 9 in order to supply a gas volume V to the measuring chamber 9 and thus to the gas space 3 of the diaphragm pressure expansion vessel 1. z with a pressure p z to supply, whereby the pressure p Z measured by the pressure sensor 15. The determination of the supplied gas volume V zis determined via the switching times of the solenoid valve 12 to the gas cartridge 13 and by means of the pressure in the gas cartridge 13 measured by the pressure sensor 15 and the pressure in the measuring chamber 8 and thus in the gas chamber 3 measured by the pressure sensor 10. For this purpose, the test device 8 further comprises an electronic measuring and evaluation unit 16, which is connected to the pressure sensors 10, 15, the temperature sensor 11, the solenoid valve 12, and the pressure regulator 14. The electronic measuring and evaluation unit 16 is connected to a battery or a power supply for power supply.

[0029] To determine the current actual pressure p ISTof the diaphragm pressure expansion vessel 1, the connecting piece 5 of the diaphragm pressure expansion vessel 1 is first shut off and the connecting line 7 of the test device 8 is connected to the gas chamber 2 of the diaphragm pressure expansion vessel 1 via the gas filling valve 6. The test device 8 then measures the current pressure p1 in the measuring chamber 8 and thus in the gas chamber 3 using the pressure sensor 10. Subsequently, the test device 8, controlled by the electronic measuring and evaluation unit 16, supplies the measuring chamber 8 and thus the gas chamber 3 with a gas volume V z with a pressure p z and thereby creates a pressure increase in the gas space 3 to a pressure p2, whereby finally from the values ​​p1, p2, p z , V Z and V N the actual form p IST is calculated in the manner described above by the electronic measuring and evaluation unit 16.

[0030] In Fig. Figure 2 shows a diaphragm pressure expansion vessel 1 with a second test device 8, which differs only in the design of the gas supply device; the reference numerals remain unchanged for identical parts. In this embodiment, the gas supply device is formed by a piston pump 17. When the gas volume is supplied to the measuring chamber 8 by the piston pump 17, the piston chamber is optionally subjected to ambient pressure or, optionally, to a defined pressure. The supplied gas volume V z is determined via the number of piston strokes or the piston stroke position and the back pressure in the measuring chamber 8 and thus in the gas space.

[0031] In Fig. Figure 3 shows a diaphragm pressure expansion vessel 1 with a third test device 8, which differs only in the design of the gas supply device; the reference numerals remain unchanged for identical parts. The gas supply device in this embodiment is formed by a compressor 18. When using a compressor 18, the supplied gas volume V z preferably determined via the compressor characteristic curve and the back pressure in the measuring chamber 8 and thus in the gas space 3.

[0032] In Fig. 4 shows a diaphragm pressure expansion vessel 1 with a fourth test device 8, which differs from the above-mentioned embodiments only in that for determining the supplied gas volume V zAn additional volume flow sensor 19 is provided in the connecting line 7, which is connected to the electronic measuring and evaluation unit 16. The gas supply device can be a gas cartridge 13, a piston pump 17, or a compressor 18. Example:

[0033] A diaphragm pressure expansion vessel 1 with the following values ​​was tested according to the measuring method described above: VN=33.73 l p1=1.355 bar p2=1.455 bar pZ=2.054 bar

[0034] From (5) we get: V1 = V2 = 33.357 I

[0035] From (7) we get: p IST = 1.439 bar

[0036] The one for p IST The determined value is greater than the pressure p1 at the start of the measurement, since the pressure is increased by the supply of the gas volume V Z was increased, the determined pre-pressure p IST is the one at the end of the measurement.

[0037] If the determined actual pre-pressure is below the target pre-pressure of the diaphragm pressure expansion vessel 1, the determined actual pre-pressure p IST If necessary, additional gas volume can then be added using the test device 8 in order to set the desired pre-pressure: P2soll=pVDsoll⋅V1V1 p VDsoll : Target form P 2soll : pressure to be set in the gas space at the end of the measurement

[0038] By generating the pressure p 2soll In the closed diaphragm pressure expansion vessel 1 the target pre-pressure p is again present VDsoll The connection piece 5 of the diaphragm expansion vessel 1 can then be unlocked.

[0039] Since the nominal volume V Nand the volume V2 in the gas space 3 are determined, the current volume in the liquid space 4 can also be determined from this. If this volume is too large, because in practice liquid is often added without determining the current pre-pressure, it is necessary to drain liquid so that the liquid can expand.

[0040] For this purpose, a vane sensor or other water flow meter with a solenoid valve for opening and closing is electrically connected to the test device 8. The water flow meter with the solenoid valve is plugged into the cap valve on the connection piece 5 of the diaphragm pressure expansion vessel 1 to discharge a defined amount of fluid in a controlled manner. The solenoid valve then closes again once the target fluid flow rate has been reached. List of reference symbols: 1 diaphragm pressure expansion vessel 2 membrane 3 Gas chamber 4 Fluid space 5 connecting pieces 6 Gas filling valve 7 Connection cable 8 Test device 9 Measuring chamber 10 Pressure sensor 11 Temperature sensor 12 Solenoid valve 13 gas cartridges 14 pressure regulators 15 Pressure sensor 16 electronic measuring and evaluation unit 17 Piston pump 18 Compressor 19 Volume flow sensor QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2016 012 700 B4

[0006]

Claims

[1] Procedure for determining the current actual pressure p IST a diaphragm pressure expansion vessel (1) which has an interior space with a known nominal volume V N which is separated by a membrane (2) into a gas (3) and a liquid space (4), wherein the filling volume of the liquid space (4) is unknown, wherein the gas space (3) of the membrane pressure expansion vessel (1) is connected to a testing device (8) and by means of the testing device (8) the pressure in the gas space (3) is changed, characterized by that the test device (8) first measures the current pressure p1 in the gas space (3), then the test device (8) adds a gas volume V z with a pressure p z and thereby a pressure increase in the gas space (3) to a pressure p2 is generated, whereby finally from the values ​​p1, p2, p z , V Z and V N the actual form p IST is calculated. [2] Method according to claim 1, characterized by that the pressure in the gas chamber (3) is increased by the test device (8) to a predetermined pressure p2 and the supplied gas volume V z measured or determined. [3] Method according to claim 1, characterized by that the test device (8) supplies the gas chamber (3) with a predetermined gas volume V Z and then the increased pressure p2 in the gas space (3) is measured. [4] Test device for determining the current actual pre-pressure p ISTa diaphragm pressure expansion vessel (1) for carrying out the method according to one or more of claims 1 to 3, having a measuring chamber (9) with a pressure sensor (10), wherein the measuring chamber (9) is connected to a connecting line (7) for connection to the gas space (3) of the diaphragm pressure expansion vessel (1) and to a gas supply device, wherein an electronic measuring and evaluation unit (16) is provided which interacts with the pressure sensor (10) and the gas supply device and is designed to carry out the method according to one or more of claims 1 to 3. [5] Test device according to claim 4, characterized by that the gas supply device is a compressor (18) or a piston pump (17). [6] Test device according to claim 4, characterized by that the gas supply device is a gas cartridge (13) connected to a solenoid valve (12). [7] Testing device according to one or more of claims 4 to 6, characterized bythat the electronic measuring and evaluation unit (16) is connected to a battery or a power supply unit. [8] Testing device according to one or more of claims 4 to 7, characterized by that it is designed for attachment to a diaphragm pressure expansion vessel (1).

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